MEMBRANE-POTENTIAL CHANGES IN SPHINCTER MOTONEURONS DURING MICTURITION IN THE DECEREBRATE CAT

Intracellular recordings from external urethral sphincter (EUS) and ex ternal anal sphincter (EAS) motoneurons were obtained during micturiti on in the decerebrate cat. The neural circuitry mediating micturition was activated by distension of the bladder or by electrical stimulatio n of the pontine micturition center (PMC). During micturition, the mem brane potential of EUS motoneurons hyperpolarized 3-9 mV, during which time the motoneuron somatic membrane conductance increased. The membr ane hyperpolarization could be reversed with passive diffusion or acti ve ejection of chloride from the intracellular microelectrode into the motoneuron. In contrast, the membrane potential of EAS motoneurons ei ther depolarized slightly or showed no change during micturition. We h ave shown that the neural circuitry mediating micturition can influenc e the EUS and EAS independently. In addition, stimulation of the PMC p rovides a valuable tool for identifying spinal neurons mediating the p ostsynaptic inhibition of EUS motoneurons during micturition.